1. Field of the Invention
The present invention relates to the control of biofilm and, more particularly, to a method and system for removing biofilm from, and/or for preventing biofilm from forming on, an interior surface of a conduit. The invention is especially suited for use with dental equipment.
2. Description of the Prior Art
As environmental agencies become more aware of the potential health risks associated with drinking either municipal or well water, there has been an ever increasing need for water purification systems that are capable of removing organics, inorganics, particulate, microorganisms, bacteria and viruses from the water supply prior to consumption. Most conventional systems require a series of filtration and chlorination units to properly remove such matters from the water.
Filtration media has been used for years to remove particulate from the water supply, while carbon block filters have been effective in removal of organics and inorganics. However, conventional filters are incapable of removing microorganisms such as bacteria, viruses, yeasts or molds. Ultraviolet radiation in the 200-300 nanometer (nm) range has been extremely effective in killing such microorganisms. As such, germicidal lamps have been used extensively in air and water purification, sewage treatment, protection of food and beverages, and other disinfection and sterilization applications.
Water purification systems that combine the disinfection and sterilization capabilities of ultraviolet radiation with the particulate, organic and inorganic filtering capabilities of conventional filter media are known. Such combined systems provide extremely pure and sterilized drinking water regardless of the origin of the water source.
Even when such water purification systems are used, however, it has been found that bacteria remains in the water and microbial biofilms can form in pipes downstream of the system. Biofilms are formed when bacteria adhere to a hard surface in an aqueous environment. Over a period of time, microbes, entering the pipe stick to an already existing bacterial layer thereby forming a microbial matrix. This matrix, once established, supplies nutrients required for growing additional microbial mass. The formation of biofilms is most pronounced in pipes formed of organic substances such as plastic and rubber, and in pipes having narrow inside diameters.
Although biofilm formation is encountered in most piping systems, the problem is particularly acute in dental unit water lines, as such water lines are usually formed of small diameter plastic tubing. Further, because the water is used in dental work, the prevention of the colonization of the dental unit water lines with bacteria is of particular importance. Nonetheless, biofilm growth has been observed inside new dental unit plastic water lines in as little as two weeks.
These biofilms, when viewed through a scanning electron microscope were found to be characterized by microorganisms embedded in an amorphous matrix of polysaccharides and glycoproteins. The observed amorphous matrix was about 30 to 50 microns thick and capable of shedding bacteria (normal size of about 1 micron) into the water supply. Pseudomonas aeruginosa biofilm quantified by measuring distributions of thickness in biofilm samples demonstrated a mean of 33 microns (range of 13.3 microns to 60.0 microns). Most biomass tend to detach in the form of multicellular particles with some particles exceeding 100 microns in size.
Large numbers of Gram-negative bacilli are commonly found to be present in the water outflow/effluent of dental units. The bacteria, which are not easily flushed out, proliferate and produce a matrix, which in turn allows the establishment of other species of bacteria. The biofilm becomes populated with a greater and greater variety of bacteria. It also protects the bacteria during their growth by retaining nutritional material and by allowing a higher level of metabolic activity, all the while protecting the bacteria from biocidal substances. The biofilm gradually becomes visible to the naked eye and can eventually partially obstruct a lumen of a water line.
Although some organisms enter a system as occasional contaminants of a main water supply, the high counts observed are due to colonization and growth on the walls of the small bore plastic tubing of the dental unit water lines.
The conventional method of eliminating biofilm in a dental unit is to fill the water lines with a disinfectant at the end of each day, allowing overnight treatment of the water lines. At the beginning of the next day, the disinfectant is drained, and water flows through cleaned water lines. This avoids contact of the disinfectant with a patient and allows a regular water supply to be used with the dental unit. However, the use of disinfectants is costly and time consuming. Also, there is a potential risk that a portion of the disinfectant will not be removed from the water lines, and will be transported to a dental handpiece and into the patient""s mouth.
U.S. Pat. No. 5,785,523 to Overmyer, entitled Dental Water Line Flushing And Disinfecting System, describes a system in which a pressurized disinfectant solution can be selectively delivered along with, or instead of water, to a dental unit. Pressurized air is directed through the water line and the dental unit to expel water. Thereafter, the pressurized disinfectant solution is introduced and preferably left in dental unit overnight. Before reuse of the dental unit, pressurized air must be directed through the system to expel the disinfectant solution.
Chlorine is the most widely used disinfectant for killing microorganisms in water and preventing the formation of biofilms. However, disinfection treatments with chlorine can produce a wide variety of by-products, many of which have been shown to cause cancer and other toxic effects.
Ozone, which is an extremely strong oxidant, is one of the most powerful water sanitizers readily available. Ozone deactivates bacteria and viruses 3125 times faster than chlorine. The prior art teaches the treatment of water with ultraviolet radiation and subsequent treatment with ozone. This prior art further teaches the use of the ultraviolet radiation source as a means for generating the ozone. Some of these prior art units have also used the ultraviolet light source to simultaneously radiate the water, and supply a source of ozone that is then entrained in the water feedstream. Introducing ozone into dental water presents a technical complexity that requires the use of an elaborate apparatus. See, for example, U.S. Pat. No. 5,935,431 to Korin, and U.S. Pat. No. 5,942,125 to Engelhard et al. Disadvantageously, ozonated water has a bitter taste, is toxic, and interferes with the curing of dental work.
There is a need for a method and system for controlling biofilm in a water line in a convenient and time-efficient manner.
There is also a need for such a method and system that minimizes the risk that a user of the water line will be exposed to a residual disinfectant.
In accordance with the present invention, a method is provided for removing biofilm from, and/or for preventing biofilm from forming on, an interior surface of a conduit that receives a supply of water. The method comprises disabling the supply of water to the conduit, and passing an ozone-containing gas to the conduit.
In accordance with one embodiment of the present invention, a system is provided for removing biofilm from, and/or for preventing biofilm from forming on, an interior surface of a conduit. The system comprises a device for disabling the supply of water to the conduit, and a device for passing an ozone-containing gas through the conduit.
In accordance with another embodiment of the present invention, a system is provided for providing disinfected water to a conduit, and for removing biofilm from, and/or for preventing biofilm from forming on, an interior surface of a conduit. The system comprises an ultraviolet lamp disposed within an ultraviolet radiation permeable sleeve such that a channel is formed between an outer surface of the ultraviolet lamp and an inner surface of the sleeve. An oxygen-containing gas is supplied to, and an ozone-containing gas is removed from, the channel. Additionally, the system includes a device for passing the ozone-containing gas to the conduit.
In accordance with yet another embodiment of the present invention, a system is provided for removing biofilm from, and/or for preventing biofilm from forming on, an interior surface of a conduit. The system comprises a source of an ozone-containing gas, an ultraviolet irradiator for (a) receiving source water and producing disinfected water, or (b) receiving the ozone-containing gas and producing an ozone-diminished gas, a device for selectively routing either the disinfected water or the ozone-containing gas to the conduit, and a device for selectively routing either the source water or the ozone-containing gas, downstream of the conduit, to the ultraviolet irradiator.